Sonoscan unveils MEMS wafer inspection system

Sonoscan has introduced its AW322 200 fully automated system for ultrasonic inspection of MEMS wafers. The system, based on the company's C-SAM technology, images and identifies internal gap-type defects down to 5um. It is intended for finding non-bonds, voids and other defects in the seals surrounding the MEMS wafer cavities.

The AW322 200 system features two loadports, two stages and multiple transducers, enabling it to image two 8in MEMS wafers simultaneously. Other models in the AW series are available to accommodate wafer sizes from 100-300mm. The SECS/GEM-enabled Robotic Handling Station includes alignment and drying operations. It also boasts the Waterfall technology to minimise water exposure during scanning. Additionally, it flaunts Sonoscan's advanced analysis software for accurate application of the user's accept/reject criteria.

In operation, the Robotic Handling Station counts and unloads wafers from the carriers, aligns wafers for scanning and positions wafers on the stage. The transducers travel over 1m/s while pulsing ultrasound at frequencies up to 230MHz and receiving thousands of return echoes per second. Both the transducers and the 500MHz bandwidth pulser/receiver were designed and manufactured by Sonoscan.

The key defects imaged in MEMS wafers are non-bonds of the seal to a wafer, voids within the seal material and other gap-type defects that can compromise the hermeticity of the cavity.

After scanning, both the acoustic wafer image and the wafer data can be used for accept/reject determination. Criteria are defined by the user with respect to acceptable defect counts and sizes.

White areas in this 230MHz Sonoscan acoustic image show incomplete (left) and complete (right) breaks in the seal around MEMS cavities.

What is a wafer?
The base unit of chipmaking. A thin circular slice of a semiconducting material, such as pure silicon, on which an IC can be formed.

What does MEMS stand for?
MEMS stands for microelectromechanical systems. They are tiny mechanical devices that are built onto semiconductor chips and are measured in micrometers. They are used to make pressure, temperature, chemical and vibration sensors, light reflectors and switches as well as accelerometers for airbags, vehicle control, pacemakers and games.